DC Crack

Hi, I'm new to the emulation scene (not the video game scene however). Having just purchased a Dreamcast, how do I go about turning it into an emulation console (esepcially for NES and Master System, and to a lesser extent, Megadrive and SNES)? I need all the basic help to get started. Do I need a mod-chip, etc.? What exactly is required in terms of hardware/software. Is there a tutorial for getting started? I know about ROMS etc., having played them at other peoples' houses, but when it comes to doing it myself, I really have no idea what's required. Any help would be much appreciated because I purchased the DC for old-school gaming (as well as the cool DC games). Thanks.